Continuous feed manufacturing systems, such as manufacturing systems used to produce paper, film tape, and the like, often include one or more motor-driven rotatable mechanical components, such as rollers, casting wheels, pulleys, gears, pull rollers, extruders, gear pumps, and the like. These systems often include electronic controllers that output control signals to engage the motors and drive the motors at pre-determined speeds. A typical controller often includes sophisticated closed-loop control circuitry that monitors the speed of the motor and adjusts the output signals to compensate for any detected error.
Web tension is one of the most critical parameters in the manufacturing and handling of web-based products. Web tension is generally related to variations in the speed of the web material as it travels through a set of driven rollers within a continuous feed manufacturing system. Conventional tension sensing devices employ various types of strain gauges, mounted onto physical beams or structures machined to enhance strain changes under tension loading. Typical configurations employ a roller wrapped by the web at an angle to translate the web tension into proportional forces on the structure. These forces, in turn, induce a strain in the gauge, allowing tension measurement.
These tension-sensing devices typically differ on methods of mounting, and methods of beam or gauge design to improve accuracy. For many applications, the required wrapping of a roller is unachievable as characteristics of the web may require that it not be contacted on its surface as it may lead to scratching, marring, smearing, and other surface finishing defects. In addition, small wrap angles reduce surface traction and the ability to drive the roller with the web, thereby increasing the likelihood of material scratching. Laminated products may have relative layer creep due to unequal path length from bending on the roller of a conventional tension sensor. Bending of thick or multi-layer constructed products can induce defects, such as delamination.
In some instances, the geometry to achieve the required wrap is awkward or impossible due to characteristics of the web or spatial limitations of the manufacturing environment. The use of highly accurate tension sensors may reduce this angle, but it is still a significant limitation. In addition, small wrap angles reduce surface traction and the ability to drive the roller with the web, thereby increasing the likelihood of material scratching.
In other instances, variations in speed have been used to determine an approximate, long-term average for web tension within continuous feed manufacturing systems. This concept, generally referred to as draw control, is well known and has been employed in web handling systems for many years. Although draw control can estimate tension at sufficiently high web speeds and over long enough measurement duration, it does not permit real-time determination of web tension. As such, draw control has not been useful within control applications that utilize web tension as a control factor. In addition, draw control is inherently an open lop strategy, i.e. the velocity of the rolls are controlled, but the tension is always estimated from the draw, and never with sufficient accuracy to control based on the measured draw. Specifically, draw techniques typically make assumptions regarding the actual web material velocity as it passes through the system. As such, position information relating to the movement of the web as it relates to velocity, tension and any other web material parameter is not obtained. No real-time estimate of web tension and its related parameters may therefore be determined using draw as the needed information is not obtained from the rollers and other system components. The present invention attempts to overcome these limitations in the prior art.